The present invention relates to a conductive sheet, a touch panel and a display device including the conductive sheet, a method for producing the conductive sheet, and a recording medium on which a program is recorded.
In recent years, electronic apparatuses including a touch panel have become widely used. The touch panel is mounted in many apparatuses including a small-size screen, such as a mobile phone or a personal digital assistant (PDA). In the future, the mounting of the touch panel in apparatuses including a large-size screen, such as a display for a personal computer (PC), is adequately expected.
As a conventional touch panel electrode, in terms of optical transparency, an indium tin oxide (ITO) is mainly used. It is known that the electric resistance per unit area of the ITO is relatively high compared with those of metals and the like. That is, in the case of the ITO, as the size of the screen (total area of the touch panel) increases, the surface resistance of the entire electrode increases. As a result, since the transmission rate of the current between electrodes is reduced, a problem that the time until the contact position is detected after touching the touch panel (that is, response speed) increases becomes noticeable.
Therefore, various techniques for reducing the surface resistance by configuring electrodes by forming a number of lattices with a thin wire (thin metal wire) that is formed of a metal with low electric resistance have been proposed (refer to Pamphlet of WO 1995/27334, Pamphlet of WO 1997/18508 and JP 2003-099185 A).
Incidentally, when the same mesh shape is regularly arrayed, there is a disadvantage in that moire (interference fringes) is easily generated in relation to pixels constituting a display screen. Therefore, various techniques for improving the visibility of an object for observation by arraying the respective mesh shapes regularly or irregularly to suppress the granular feeling of noise (also referred to as feeling of roughness) have been proposed.
For example, as shown in FIG. 46A, JP 2009-137455 A ([0029]) discloses a window for a movable body for riding including a mesh layer 4 and the pattern PT1 of the shape thereof in plan view. In the mesh layer 4, an arc-shaped conductive wire 2 obtained by eliminating a part of the circle is repeatedly disposed in a lattice shape and the end of the arc-shaped wire 2 is connected near the center of the adjacent arc-shaped wires 2. JP 2009-137455 A describes that not only visibility but also the electromagnetic wave shielding property and the resistance to breakage can be improved thereby.
As shown in FIG. 46B, JP 2009-16700 A ([0022] to [0024]) discloses a transparent conductive substrate produced using a solution that forms a mesh-like structure on a substrate naturally when left after being coated on one surface of the substrate, that is, a self-organizing metal particle solution, and the pattern PT2 of the shape thereof in plan view. JP 2009-16700 A describes that the irregular mesh-like structure, which does not cause a moire phenomenon, is obtained thereby.
As shown in FIG. 46C, JP 2009-302439 A ([0011] to [0015]) discloses a light-transmissive electromagnetic wave shielding material and the pattern PT3 of the shape thereof in plan view. In the material, an electromagnetic wave shielding layer 6 has a structure of a sea region of a sea island structure and the shapes of island regions 8 as openings surrounded by the electromagnetic wave shielding layer 6 are mutually different. JP 2009-302439 A describes that thereby, the optical transparency and the electromagnetic wave shielding property are improved without occurrence of moire.
However, when further reducing the granular feeling of noise and improve the visibility in the patterns PT1 and PT2 disclosed in Patent Literatures 4 and 5, there is a structural problem of the patterns.
For example, in the mesh-like pattern PT1 disclosed in JP 2009-137455 A, the arc-shaped wire 2 is repeatedly disposed in a lattice shape. Accordingly, the periodicity of the wire 2 is very high. That is, when the power spectrum of the pattern PT1 is calculated, it is predicted that a sharp peak is present in a spatial frequency band corresponding to the inverse of the arrangement interval of the wire 2. Here, in order to further improve the visibility of the pattern PT1, it is necessary to reduce the size (diameter) of the arc of the wire 2.
In the mesh-like pattern PT2 disclosed in JP 2009-16700 A, the shape or size of the mesh is irregular, and accordingly, irregularity is very high. That is, when the power spectrum of the pattern PT2 is calculated, it is predicted that an approximately fixed value (close to white noise characteristics) is obtained regardless of a spatial frequency band. Here, in order to further improve the visibility of the pattern PT2, it is necessary to reduce the size of self-organization.
Therefore, in both the patterns PT1 and PT2, when further improving the visibility, there is a disadvantage in that the light transmittance or productivity is reduced.
Further, the pattern PT3 disclosed in JP 2009-302439 A does not form a mesh shape. Accordingly, a variation occurs in the wiring shape of the cut edge. Therefore, when the pattern PT3 is used, for example, as an electrode, there is a disadvantage in that stable current transmission performance is not obtained.